Determination of the quality of a gas

ABSTRACT

A procedure for the determination of the quality of gas of a probe gas, in particular a burnable gas, using a transmission spectrum of the probe gas determined at operating conditions by means of spectroscopical methods of measurement. At least the associated values of the pressure p and the temperature T of the probe gas are determined and in a number of selected spectral regions at least one spectral vector is constituted by integrating quantities of the transmission spectrum of the probe gas, which shows as components the values of the integrals with respect to the selected spectral regions and is characteristic for the properties of the probe gas at operating conditions. Afterwards, for the determination of a physical quantity according to the quality of gas, the spectral vector is multiplied with a factor vector, which has been evaluated by means of calibrating measurements of spectral vectors of calibrating gases of known features and under known conditions of state, in which with respect to the physical quantity to be determined according to the quality of gas, a respective factor vector is brought in.

CROSS-REFERENCE TO RELATED APPLICATIONS

Applicant claims priority under 35 U.S.C. §119 of German Application No.199 49 439.8 filed Oct. 14, 1999. Applicant also claims priority under35 U.S.C. §120 of PCT/DE00/03572 filed Oct. 11, 2000. The internationalapplication under PCT article 21(2) was not published in English.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention concerns to a procedure for the photometric determinationof the quality of gas, particularly of burning gases, according to theprecharacterising part of claim 41.

2. The Prior Art

For determining the quality of gas for example in distribution networksfor natural gas or the like, devices for measuring the quality of theguided-through gases are used. These devices measure the condition ofgas. Natural gas, because of being a natural product according to itsorigin and by mixture shows respective fluctuations in respect of itscomposition, whereas the composition for example of natural gas comingfrom the different hydrocarbons determines the caloric value fromextrapolated quantities. Therefore it is of great importance to measurethe guided-through amount of gas in a gas supply network and therewiththe respective amount of energy, to determine the exact respectivecondition at the feeding point into the natural gas network and at thedeliverance points of the customers and therewith to deduct a definitetransported or supplied amount of energy. In doing so for the customerof the gas, an invoice can always state the actual supplied amount ofenergy relating to different conditions of the gas and a correspondinglyvarying amount of energy. Vice versa, the detection of the condition ofthe gas offers the guarantee for the customer to obtain a desiredquality and therewith a required amount of energy.

The determination of the quality of gas obtains additional relevance,since with the elimination of the guiding-through monopoly, thesuppliers of natural gas use the same network for delivering gases ofquite different provenance and therefore also different composition.Only an easy and cost-effective detection of the condition of the gas bymeans of cost-effective measuring devices and methods allows for acontrollable and accurate accounting.

For the measurement of the quality of gas as relevant quantities, thestandard volumetric gross calorific value H_(v,n), the standard densityρ_(n) and the compressibility coefficient K have to be determined asaccurately as possible and also regarding the different gas qualities.

In practice, for the settlement of account, the transported volume Vb ofthe of the gas at working conditions (pressure p_(b), temperature T_(b))is measured by means of flow measuring devices. With knowledge of thecondition of the gas, the compressibility coefficient K can bedetermined, with which the volume of the gas V_(n) at standardconditions (pressure p_(n), temperature T_(n)) is calculated.$V_{n} = {\frac{p_{b}T_{n}}{p_{n}T_{b}}\quad \frac{1}{K}V_{b}}$

By means of multiplication of this standard volume with the volumetricgross calorific value H_(v,n) at standard conditions, the transportedamount of energy Q can be obtained:

Q=V _(n) H _(v,n)

Alternatively, the volume at working conditions V_(b) can directly bemultiplied with the volumetric gross calorific H_(v,b) at workingconditions (Energymeter).

Another important quantity for applications with natural gas is thethermal output of gas burners; this varies in accordance to the gasquality and is characterized by means of the so-called Wobbe index Wv:gases with the same Wobbe index Wv deliver the same thermal output at aburner nozzle. For calculating the Wobbe index Wv the standard densityρ_(n) of the gas is required, from which the relative density accordingto air is determined (dv=ρgas/ρair) $W_{v} = \frac{H_{v}}{\sqrt{d_{v}}}$

Therefore the determination of the gross calorific value H_(v,n) atstandard conditions has central relevance for the practicaldetermination of the quality of gas, for example, for accountingpurposes.

Until now different devices for the measurement of the gas quality areused. So-called direct and so-called indirect procedures are known. Byusing direct procedures, the quantities to be determined are measuredseparately and therefore the gas is transformed to standard conditions,by which expensive treatments of the gas are required.

The gas condition can be determined most easily by means of so-calledcalorimeters, in which by means of an open flame a gas probe is burntand submitted to a cooling medium. Heat quantity and the thereupondetectable temperature rise of the cooling medium the calorific value ofthe burnt gases can be determined. Such devices will need a complicatedmechanic for the adjustment of a certain quantitative proportion of gas,combustion air and for example cooling air as cooling medium and aretherefore expensive and error prone, and enhanced security requirementsfor the devices are necessary due to the open burning. Also themaintenance and calibration have to be carried out by qualifiedpersonnel, and the calorimeter must be used in conditioned rooms.Therefore the purchase and operating costs of such test assemblies arevery high.

Using calorimetry by means of catalytic burning (for example withpellistors) the probe gas is mixed with air and burnt at the 400 to 500°C. hot helixes of a catalyst. The temperature rise of the catalyst isabout proportional to calorific value. Because this procedure is basedon a sensitive surface effect, it is subject to strong drifts andnecessitates frequent calibration with search gas. The catalyticcalorimeter is most favorable of all mentioned procedures, however,because it is better suited for control than for accounting because ofits accuracy.

The direct measurement of the density ρ_(b) at working conditions isdone with hydrostatic balances, which are very expensive precisiondevices, with which the buoyancy of a ball filled with nitrogen ismeasured in accordance to the density of the surrounding medium, here ofthe probe gas. With another procedure a thin-walled metal cylinder,which is positioned by a current linkage of the probe gas, is set inoscillation. The density of the surrounding gas determines the resonantfrequency of the cylinder, which is captured as a sensitive measuredquantity. Both procedures are very expensive for the determination ofthe standard density, because you they require an adjustment to thestandard conditions.

The compressibility coefficient K cannot be measured directly, butinstead can be calculated by means of different numericalstandard-arithmetic techniques out of the directly measurable gasquantities. One of these procedures, the so-called GERG88-procedure(DVGW-worksheet 486) needs the input quantities listed in table 1 below.The amount of substance of CO₂ is determined according to the state ofthe art by a non dispersive infrared-spectroscopical procedure (NDIR),whereby the gas must be brought into a defined condition near or atstandard conditions. The amount of substance of H₂ is of significanceonly when working with coke oven gases and can be left unattended in thetypical natural gases today distributed in Europe. The compressibilitycoefficient K can be determined to 10⁻³ with the help of theGERG88-equation in case of sufficient accuracy of the input quantities.

TABLE 1 input quantities of the GERG88-procedure P_(b) pressure atworking conditions T_(b) temperature at working conditions ρ_(n) densityat standard conditions H_(v,n) volumetric gross calorific at standardconditions xCO₂ amount of substance of CO₂ xH₂ amount of substance of H₂

The other procedure for determination of the behavior of real gases isdone according to the AGA8-92DC-equation (ISO 12213-2:1997 (E)). Thisprocess requires as input quantities the amount of substance of 21leading gas components (table 2) and has an accuracy of 10⁻³.

TABLE 2 input quantities of the AGA8-92DC-equation methane CO₂ ethane N₂propane H₂S isobutane He n-butane H₂O isopentane O₂ n-pentane Arn-hexane H₂ n-heptane CO n-octane pressure n-nonane temperature - decylhydride

The state of the technology includes, besides the direct measurementtechniques, also the indirect measurement of the gas quality by means ofgas chromatography. A defined volume of the probe gas is brought into adefined condition and is carried by a carrier gas, typically helium,through a system of gaschromatographic separation columns. Due to theirdifferent retention times, the individual gas components reach thedownstream sensor, generally this is a detector for caloricconductibility, at the end of the separation column at different times.The peak area of the sensor signal can therefore be interpreted asamount of substance, whereas the evaluation must be carried out incomparison with a reference gas, that must have a similar composition tothe probe gas.

The drawback of the gas chromatography is the expensive samplepreparation and installation of the whole system, and the expensivemaintenance and operation by well-trained personnel. From the amounts ofsubstances of the individual gas components that the gas chromatographydelivers, all relevant gas quantities can be calculated. For theimplementation of such indirect measurements via chromatography,automatically working process chromatographs with detectors for caloricconductability are deployed. These devices generally measure elevencomponents of the natural gas (N₂, CO₂, CH₄, C₂H₆, C₃H₈, C₄H₁₀, C₅H₁₂,C₆+ and so on) Helium is used as the carrier gas, but its lightvolatility in practice often leads to prematurely emptying of the bottlefor the carrier gas and therefore leads to short maintenance cycles forsuch a device. A gas is chosen as the calibrating gas that is similar tothe natural gas to be measured.

Such chromatographic systems carry out measurement cycles withoutinterruption, in order to capture changes in the quality of the gasimmediately. This leads to a high consumption of carrier gas andcalibrating gas and requires that maintenance of the device be performedin relatively short intervals.

It is also known to determine the composition of a gas with conventionalinfra-red-gas-analyzers. Such analyzers working in the middle infra-redor near infra-red area do not offer the requirements of high precisionand stability for a determination of the caloric value under themeasurement conditions which are required here.

Also, a parallel reference measurement must be carried out beside theintrinsic measurement of the probe gas, for the sake of compensating theat least essential influences of failures. As a measuring result, theknown infra-red-gas analyzers deliver superimposed frequency spectrums,that make it very difficult to form a conclusion regarding individualcomponents of a inspected gases.

In the literature there has been described an infrared spectroscopicalprocedure for gas analysis (Optical BTU sensor Development,” GasResearch Institute GRI-93/0083), that determines by means of-so-calledmultivariate analysis (MVA) of the near infrared spectrum of gases thevolumetric concentration of the amount of substances of thecarbon-containing components of the gas and therewith of the volumetriccaloric value under operating conditions. This procedure does notdeliver the calorific value H_(v,n) under standard conditions or thestandard reference density ρ_(n) and the amount of substance of CO₂, sothat it is not qualified for the determination of the compressibilitycoefficient K nor the complete determination of the quality of a gas.Determining the calorific value by means of known photometric methodsrequires necessary equipment for the realization of the procedures,whereby a benefit in the speed of the coverage of the absorptionspectrums of the natural gas in near or middle infrared spectral area isobtained. The entire absorption spectrum of the natural gas is thereforeput together from of the sum of single spectrums of componentsrepresented in gas and therefore can be measured and analyzed with theaid of more appropriate methods of spectral analysis.

Doing this, the ascertained quota of extinction of a component in theentire spectrum of the natural gas is equivalent to the part of theconcentration of this component within search gas (so-calledBeer-Lambert-law). With the knowledge of the calorific value of thisrespective component, the calorific value of the entire mixture of gasescan then be calculated as a summation value. This procedure of spectralanalysis has the problem, however, of the intense overlap by absorptionbands of different components, which frequently lead to inaccurateresults and beyond that to a high calculation effort. One more infraredspectroscopical procedure according to DE 198 38 301 A1 acts as a directspectral evaluation (DSA) with a spectral function, with which thespectrum of the gas is folded. The procedure allows the specification ofthe volumetric calorific value H_(v,b) under operating conditions directfrom the spectrum. While burning the gas, the respectively caused heatof the reaction is based on the combustion of C—H-bindings and a therebycaused heat quantity depends to the present binding energy. This isthereby exploited, that the oscillations of the C—H-bindings, which areequal to each other, have a certain binding energy and produce the sameheat quantity during a combustion, interact with an associatedwavelength of an electromagnetic radiation. It is possible by means of awavelengths-resolved measuring and a wavelengths-dependent valence ofthe grade of interaction of these oscillations to calculate thecalorific value H_(v,b) of the gas, without the requirement of anidentification of individual gas components. This document additionallydiscloses a device for the realisation of such a procedure, which istuned for the specific requirements of the measuring method and enablesa weighted summing up of the grades of interaction. With this procedure,the calorific value H_(v,b) of a mixture of gases under operatingconditions can be determined, the other quantities relating to thedetermination of gas quality can itself not be determined with measuringtechniques.

It is further known a procedure according to DE 199 00 129.4 A1, inwhich the density of a probe gas at working conditions is determinedwith an optical-spectroscopical procedure. This procedure proceeds onthe assumption, that each binding of the IR-active gas componentscontributes to the extinction, whereby with each binding the mass of thecoupled atoms is associated. In this manner, the mass of all theIR-active atoms is represented by contributions to absorption within thespectrum. The frequency of oscillation of each binding and therewith itsspectral location depends on the reduced mass of the partners ofbinding. The spectrum contains in its amount and its spectraldistribution information for determination of the density of the gas.The context between the spectrum and the mass in the measuring volumeand therewith with the density at working conditions of the gas isdescribed by a spectral weighting function, which can be called spectraldensity. The contribution of masses of the IR-inactive components willbe calculated via the stated quantities and an appropriate formulationfor the compressibility behaviour. In such a procedure, multipleiterations are required, for which certain assumptions with regard tothe initial conditions must be taken, which possibly can be problematicwith regard to the convergence of the iteration.

SUMMARY OF THE INVENTION

Therefore, it is object of the present invention to suggest a procedurefor the determination of the quality of gas, with which the quantitiesrelevant for the quality of gas can be determined by means of aspectroscopical detection of the quality of gas, as well as respectiveevaluations. The invention comprises a procedure for the determinationof the quality of a probe gas, in particular a burnable gas, in which atoperating conditions by means of spectroscopical methods of measurementa transmission spectrum of the probe gas is determined. In a first step,at least the associated values of the pressure p and the temperature Tof the probe gas are determined. In a further step, in a number ofselected spectral regions at least one spectral vector is created byintegrating quantities of the transmission spectrum of the probe gas.The spectral vector has as components the values of the integrals withrespect to the selected spectral regions and which are characteristicfor the properties of the probe gas at operating conditions. In afurther step, a physical quantity to be determined in that spectralvector is multiplied with a factor vector. The factor vector has beenevaluated by calibrating measurements of spectral vectors of calibratinggases having known features and under known conditions, in which inrespect to the physical quantity to be determined a respective factorvector is brought in. In this way, the physical quantity to bedetermined according to the quality of gas is measured directly byinclusion of the state of the probe gas by evaluating the spectrum andwithout iteration. By connecting the data for the pressure p and thetemperature T derived out of the measuring of the state of the probe gaswith the spectral vector, which is derived out of the transmissionspectrum, the quantities of the probe gas at operating conditions can betranslated to technically better usable standard quantities, especiallythe gross calorific value H and the density ρ.

The spectral vector, which is derived from the transmission spectrum, ishereby determined by the integration of the measured values of theextinction of the transmission spectrum, in which these integrals areonly determined in selected spectral regions. The spectral vector istuned in correspondence to the usual components included in thecomposition of the probe gas to be examined. Therefore, the spectralvector is characteristic for the composition of the probe gas in thespecific operating state in question. Because the operating state of theprobe gas is a not insignificant influence to the transmission spectrumof the probe gas, this factor of influence is taken into considerationin determining the transmission spectrum in the operating state of theprobe gas by means of the factor vectors, which are determined bycalibration measurements of spectral vectors of definite calibrationgases, whose composition and therefore the nominal transmission spectrumis known. These factor vectors are determined by simultaneousmeasurement of the present state conditions, so that the influence oftemperature T and pressure p of the transmission spectrum of calibrationgases is known. These factor vectors can therefore be carried out byscalar multiplying, which is simple to carry out and needs no iterationsteps, with the spectral vector determined by means of simplemathematical operations. With respect to the quantity to be determinedaccording to the quality of gas, a correlated factor vector derived fromthe calibration measurement can be brought in. Therefore a high accuracywith this procedure according to the invention can be obtained for abroad region of the state of the probe gas, in which the influence ofthe quantities of the state can be compensated.

A first embodiment of the invention provides that the factor vectors aredetermined in advance in a definite measurement environment by means ofcalibrating measurements, which are carried out with calibrating gasesof known features and under known conditions of state. Such a definitemeasurement environment offers as well the possibility to determine thetransmission spectrum being the base of the calculation of the factorvectors as well as the state quantities temperature T and pressure pwith a high accuracy, which can not be obtained by carrying out theprocedure in the field with arguable costs. The factor vectors arehighly accurate correction values for the influence of the measurementof the transmission by the operating state of the probe gas, in whichthe factor vectors can be determined three-dimensional and by timeseparated of the determination of the spectral vectors.

There are advantages, that during the calibrating measurements thefactor vectors are determined in the form of a characteristic mapping bythe variation of pressure p and temperature T of the used calibratinggases. With this method, it is possible to determine for broad regionsof the changes of pressure p and temperature T the according factorvectors in advance and to place them at disposal for the scalarmultiplying with the spectral vector. The changes of the transmissionspectrum due to the pressure p, the so-called pressure broadening, asalso the changes in accordance with the temperature can be taken intoconsideration.

Furthermore, variations of the operating point of the measuringapparatus according to the operating state of the probe gas can becompensated. These variations occur, for example, in a spectrometerbecause of the variation of the density of the particles in the area inthe measuring beam. Also, real gas effects of the probe gases whichbehave themselves not as an ideal gas, can be compensated, so that thedensity of the particles in the area in the measuring beam is notdirectly proportional to the quotient of pressure p and temperature T.The calibration by means of the calibration gases is caused by a seriesof definite operating states in a phase field and for a suitable set ofcalibrating gases, so that as a result, a factor vector characteristicmapping (p,T) for each measuring quantity is obtainable, that is fixedby the quantity of operating.states pressure p and temperature T.

There is a special advantage, if for each of the physical quantities tobe determined in respect to the quality of gas, a respective factorvector coming from the characteristic mapping for a state of the probegas is determined. Figuratively speaking, for each of the physicalquantities to be determined with respect to the quality of gas derivedfrom the characteristic mapping (p,T), a projection onto the respectiveplane of the quantity to be determined is carried out, so that for eachquantity to be determined, an especially resulting factor vector can bedetermined.

Because of the connection of the quantity of operating states pressure pand temperature T during the recording of the spectral vector, there isa further advantage, if, for constituting the scalar product with therespective according spectral vector that factor vector is chosen fromthe characteristic mapping, which corresponds to the state quantities ofthe probe gas during the recording of the spectrum of the probe gas andto the physical quantity to be determined with respect of the quality ofgas. By means of this assignment of the factor vector to the quantitiesof operating states pressure p and temperature T of the probe gas, aconsiderable compensation of the influence of the quantities ofoperating states to the transmission spectrum takes place.

Also it is conceivable, that for each physical quantity to be determinedwith respect to the quality of gas, at least one spectral vector has tobe constituted, in which the so constituted spectral vectors can beconstituted from values coming from spectral regions with differentboundary wavelengths and/or different sizes of spectral regions and/or adifferent numbers of spectral regions. With respect to the physicalquantity to be determined with respect of the quality of gas, it can beadvantageous to determine appropriate adapted spectral vector, becausespectral regions adapted respectively to their position and magnitude inthe spectrum or their number allow a higher accuracy of the measurement,as it would be possible with similar spectral regions for all physicalquantities to be determined with respect to the quality of gas.Therefore, in a further development for the constitution of everyphysical quantity to be determined with respect to the quality of gas,different spectral regions can be brought in.

Also it important that the number and position of the spectral regionsof each scalarly multiplied spectral vector and factor vector correspondto each other. Only in this way a physically correct result can beobtained, so that during determination of the characteristic mapping ofthe factor vectors a series of characteristic mappings is to bedetermined with spectral vectors which are based respectively on otherspectral regions.

A special preferred embodiment of the procedure according to theinvention provides that for the determination of the physical quantityto be determined with respect of the quality of gas, a separationformulation is carried out, in which one part of the physical quantityto be determined is varied essentially with the composition of the probegas and another part is influenced only slightly by the state of theprobe gas and by the composition of the probe gas. The part which isinfluenced by the state of the probe gas can be calculated by means ofdetermined state data coming from a known average gas, whereas the partwhich varies essentially with the composition of the probe gas isdetermined from the transmission spectrum of the probe gas. By means ofthis separation into two parts according to the separation formulationit is possible to increase the accuracy of the determination of thephysical quantity to be determined with respect of the quality of gas.

In a first embodiment, the physical quantity to be determined withrespect to the quality of gas, the compressibility coefficient K of theprobe gas can be determined. A further embodiment provides that as thephysical quantity to be determined with respect to the quality of gas,the compressibility factor Z of the probe gas is determined. Also it isconceivable, that as the physical quantity to be determined with respectof the quality of gas, the density R of the probe gas and/or the Wobbeindex Wv and/or the methane factor and/or the molar mass and/or the dewpoint of the probe gas is determined.

In a further embodiment it is conceivable, that as physical quantity tobe determined with respect of the quality of gas, the density of thepart of carbon dioxide of the probe gas is determined, from whichafterwards by usage of the directly determined real gas behaviour, forexample the compressibility coefficient K or the real gas factor Z, themol fraction XCO₂ can be calculated, that means the quota ofCO₂-molecules in the probe gas. Therewith also the density of carbondioxide in an operating state can be translated to the appropriatecarbon dioxide mol fraction XCO₂. This CO₂-concentration, which isneeded in procedures of conventional gas measuring techniques as one ofthe input values for the calculation of the compressibility coefficientK, for example, according to the procedure SGERG, can also be determineddue to reasonable compatibility by means of the procedure according tothe invention. Also, it is possible with this measuring of theabsorption due to carbon dioxide CO₂ derived from the transmissionspectrum, to obtain an increase of the measuring accuracy of the otherquantities to be determined with respect to the quality of gas, becausethey deliver further information about the mixture of the not burnablecomponents of typical probe gases such as nitrogen and carbon dioxide.

There is a special advantage if the transmission spectrum of the probegas is recorded in the region of infrared light, preferably in theregion of the near-infrared. In this spectral region, radiation sources,detectors and further optical components are cheap and deliverable onthe market in high numbers and high quality, so that the neededmeasurement techniques for carrying out the procedures can beconstructed inexpensively.

A first embodiment provides, that as spectral regions at least parts ofthe transmission spectrum in the region between about 1550 nm and 2050nm are used. A capture of the influences of the probe gas to thetransmission spectrum in selected sections of such a broad spectralregion allows a considerable adaptation and tuning of the procedureaccording to the invention to respective probe gases in question, whichcan be influenced within the bounds of calibration measurement fordetermination of the factor vectors.

In a further embodiment, as the spectral region for the determination ofthe part of methane CH₄, which can be found proportionally mostfrequently in burnable gases, radiation at about 1620 to 1660 nm isusable, in which these and the following data of the spectral regionsshall be emphasized only as preferred and by means of practicalmeasuring most effective spectral regions. It is directly to beunderstood, the in case of other compositions of gas or other managingof processes in between of the previously mentioned regions other orfurther spectral regions can be elected. For the determination of theparts of the sum of all aliphatic hydrocarbons as the spectral region,radiation at about 1670 to 1770 nm can be used. Also it is conceivable,that for the determination of the part of carbon dioxide CO₂, radiationat about 2000 to 2020 nm can be used. The preceding values for thespectral regions all lie in a region of the first harmonic overtone bandof the molecule oscillations and offer therefore special fine conditionsfor a correct capture of the quantities to be determined with respect tothe quality of gas. Of course, measurements can be carried out in theregion of further overtone oscillations, but also of the fundamentalwave.

During the constitution of the scalar product, a correcting function isincluded, which takes into consideration the equipment differencesbetween the measurement arrangement during the determination of thefactor vectors with the calibrating gases and the measurementarrangement during the determination of the spectral vector of the probegas. Such a correcting function takes into consideration the equipmentdifferences between a high-accuracy calibration measurement arrangementand the measurement arrangements designed for practical usage, whichmust, besides scatter because of technical equipment, make cuts inaccuracy. Therefore in the scope of calibrating each single apparatus,which is determined for the implementation of the procedure according tothe invention, it is adjusted, and differences between the respectiveapparatus and the calibration measurement which exist, is taken intoconsideration as a correcting factor for the results of thedetermination of the transmission spectrum. By this, it is also alwaysguaranteed in the case of manufacturing of respective apparatuses inseries production, that a difference resulting from the seriesproduction is captured and can be compensated. Calibration is dividedinto master-calibration and specimen-calibration: With a master-specimenof the measuring apparatus typical for a design, a measurement ofrespective spectral vectors is carried out in a wide field of welldefined states and a suitable set of well-defined calibration gases andthere form the calculation of the respective factor vectors. Thedetermination of the spectral apparatus constant of the single serialspecimen of the design is then carried out via measurement of only oneor a less amount of calibration gases and comparison of the differenceto the respective master-calibration.

There is a special advantage, that as source for the radiationpenetrating the probe gas during the recording of the transmissionspectrum broadband, radiators, especially thermal radiators, can beused. The radiators capture the transmission spectrum by usage ofinterference filters and/or a monochromator and/or optical detectors andprepare it in the sense of measuring techniques in such a manner, thatthe input values for the procedure according to the invention can bederived. It can also be conceivable, that as a source for the radiationpenetrating the probe gas during the recording of the transmissionspectrum, narrow-band radiators, especially light-emitting diodes (LED)or sources of laser light, are used, if their spectral characteristicscan be suitably adjusted.

A further simplification of the procedure according to the invention isobtainable, if the boundary wavelength of the chosen spectral regionsduring the recording of the transmission spectrum are determined bymeans of appointing the boundary wavelength relative to a referencesignal. While recording the spectrums according the procedure inquestion, the spectral position of the bands relative to the boundariesof the chosen spectral regions have a great influence for the accuracyof the evaluation. In common laboratory spectrometers as typicalmeasurement arrangements, the absolute accuracy of wavelength isguaranteed by means of a high expenditure with respect to the mechanicalworkmanship and by usage of reference wavelengths (interference filters,laser). For avoiding this high technical expenditure for seriesarrangements, the absolute position of the wavelength can be determinedby means of a characteristic position of the reference signal andcorrected reference to the axis of the wavelength. In case of analyzing,for example, natural gas as probe gas, in a further development as areference signal, the region of the best absorption of the radiation ofmethane, the so-called absorption peak of methane at about 1666 nm isoffered. This maximum is best qualified for the correction, becausemethane as guiding component always dominates in natural gas and thehigh coefficient of extinction of this maximum allows for gooddetection. The position of this maximum is evaluated and, relative tothis maximum, the position of the boundary wavelengths of the chosenspectral regions are adjusted. With this, the requirements for theabsolute accuracy of the wavelength of respective measurementarrangements can be reduced substantially. The resulting error ofwavelength depends rather on the limited reproducibility of thewavelength adjustment. In a further development it is conceivable, thatalternatively as reference signal typical gradients of spectrums ofmediums are used, which are placed additionally in the beam path of thearrangement for measuring the transmission spectrum, as this can becarried out in the form of plastic foils, that are placed in thereference beam path of the measuring arrangement.

A further increase of the accuracy of the procedure according to theinvention can be obtained, if among other spectral regions, in which thetransmission spectrum of the probe gas contains information about itscomposition, spectral regions are surveyed, in which no absorption bythe probe gas occurs. Such a survey of additional spectral regions isimportant during the practical usage of the measurement arrangement inrespect of the long-time stability, because there may be variations inthe blank transmission of the measuring channel, which are notestablished because of changes of the probe gas and therefore falsifythe measurement result. The spectral regions which are not or not asmuch influenced by the composition of the probe gas therefore can, in afurther development, be used for the self-control of the measurement ofthe probe gas in the form of a reference, in which in a first embodimentfor calibration of the measurement arrangement essentially at everyrecording of a transmission spectrum of the probe gas or in a frequentsuccession a measurement in the absorption free spectral region of theprobe gas is carried out. For these purposes, for example, at eachrecording of a spectrum region also an absorption free spectral regioncan be recorded, in which the measurement arrangement after therecording of the spectral regions carried out with the procedureaccording to the invention again carries out a measurement in the regionnot depending on the spectral region of the probe gas and compares thetherein determined transmission with the respective latest measurementin this spectral region. If such a change in transmission in a regionnot depending on the spectral region of the probe gas goes beyond agiven limit, than in further development a blank measurement of themeasuring arrangement with a absorption free spectral region for, e.g.,natural gas can be carried out to compensate for the measurementconditions. In this way, an automatic self control of the measuringsystem can be carried out.

Another embodiment provides that the difference of at least one of thepreceding measurements underneath a given threshold value is taken intoconsideration as correction factor for the measurements for thedetermination of the physical quantities to be determined according tothe quality of gas. In this way, an improvement of the measuring resultsduring the actual usable measurement can be obtained by the evaluationof the determined differences.

A very advantageous spectral region for the transmission in generalindependent of the composition of the probe gas is positioned in theregion of about 1500 to 1600 nm.

A further embodiment provides, that one or several of the physicalquantities to be determined according to the quality of gas aredetermined only by means of calculation by usage of quantities derivedfrom the transmission spectrum by constitution of the scalar product insuch a manner. The physical quantities determined via measurement andcalculation describe and essentially correct the real gas behaviour ofthe probe gas by the way of inserting them in standardized approximatemethods. For example the transmission spectrum for the measuring of thepart of CO₂ in the probe gas is evaluated in a region above 2000 nm, soexpensive and fault susceptible sensors are needed, which allowmeasurements in this high region of wavelength. Such sensors cost morethan measuring equipment in the region up to 1800 nm, so that thenecessary measuring arrangement for carrying out the procedure accordingto the invention with incorporation of the part of CO₂ is significantlymore expensive as a measuring arrangement, for example, if only for thecapture of burnable gases of a probe gas.

For establishing a compatibility with apparatuses of the commontechniques for measuring gases, the part of carbon dioxide in the probegas can be determined only by calculation in such a way, that using theprocedure according to the invention the real gas behaviour and furtherphysical quantities to be determined according to the quality of gas aredetermined by the scalar product of the spectral vector and factorvector. The component, which is not determined with measuringtechniques, for example the part of carbon dioxide, can be calculatedfrom the quantities derived as described above in such a way, that bymeans of reversal of a standardized procedure as for example theprocedure SGERG or the same after application of the respectiveprocedure results in the correct real gas behaviour. With the procedureaccording to the invention, a sufficiently exact determination of thequota of carbon dioxide is available, without complicating or making theprocedure much more expensive because of its equipment conversion.

What is claimed is:
 1. A procedure for determining quality of a probegas, comprising: determining a transmission spectrum of the probe gas atoperating conditions by spectroscopical methods of measurement;determining pressure p and temperature T of the probe gas; determiningat least one spectral vector {overscore (S)} in a number of selectedspectral regions by integrating quantities of the transmission spectrumof the probe gas, the spectral vector having as components values ofintegrals with respect to the selected spectral regions and beingcharacteristic for the properties of the probe gas at operatingconditions; and multiplying said spectral vector {overscore (S)} with afactor vector {overscore (V)}, said factor vector {overscore (V)}determined by calibrating measurements of spectral vectors {overscore(S)} of calibrating gases having known features and under knownconditions, in which a respective factor vector {overscore (V)} is usedto determine a physical quantity based on the quality of the gas,wherein during calibrating measurements, the factor vectors {overscore(V)} are determined in the form of a characteristic mapping by avariation of pressure p and temperature T of the calibrating gases. 2.The procedure according to claim 1, wherein for each physical quantityto be determined, a respective factor vector {overscore (V)} coming fromthe characteristic mapping is determined.
 3. The procedure according toclaim 1, wherein for multiplying with a respective spectral vector{overscore (S)}, a factor vector {overscore (V)} is chosen from thecharacteristic mapping, said factor vector corresponding to thequantities of the probe gas during recording of the spectrum of theprobe gas and to the physical quantity to be determined.
 4. A procedurefor determining quality of a probe gas, comprising: determining atransmission spectrum of the probe gas at operating conditions byspectroscopical methods of measurement; determining pressure p andtemperature T of the probe gas; determining at least one spectral vector{overscore (S)} in a number of selected spectral regions by integratingquantities of the transmission spectrum of the probe gas, the spectralvector having as components values of integrals with respect to theselected spectral regions and being characteristic for the properties ofthe probe gas at operating conditions; and multiplying said spectralvector {overscore (S)} with a factor vector {overscore (V)}, said factorvector {overscore (V)} determined by calibrating measurements ofspectral vectors {overscore (S)} of calibrating gases having knownfeatures and under known conditions, in which a respective factor vector{overscore (V)} is used to determine a physical quantity based on thequality of the gas, wherein for each physical quantity to be determinedwith respect to the quality of the gas, at least one spectral vector{overscore (S)} must be created from values coming from spectral regionswith different boundary wavelengths or different sizes of spectralregions or different numbers of spectral regions.
 5. Procedure accordingto claim 4, wherein different spectral regions are used for everyphysical quantity to be determined.
 6. Procedure according to claim 4,wherein a number and position of the spectral regions of each multipliedspectral vector {overscore (S)} and factor vector {overscore (V)}correspond to each other.
 7. Procedure according to claim 4, wherein theselected spectral regions comprise at least parts of the transmissionspectrum in the region between about 1550 nm and 2050 nm.
 8. Procedureaccording to claim 4, wherein the spectral region for determination of apart comprising methane CH₄ radiation is at about 1620 to 1660 nm. 9.Procedure according to claim 4, wherein the spectral region fordetermination of a part comprising a sum of all aliphatic hydrocarbonradiation is at about 1670 to 1770 nm.
 10. Procedure according to claim4, wherein the spectral region for determination of a part comprisingcarbon dioxide radiation is at about 2000 to 2020 nm.
 11. A procedurefor determining quality of a probe gas, comprising: determining atransmission spectrum of the probe gas at operating conditions byspectroscopical methods of measurement; determining pressure p andtemperature T of the probe gas; determining at least one spectral vector{overscore (S)} in a number of selected spectral regions by integratingquantities of the transmission spectrum of the probe gas, the spectralvector having as components values of integrals with respect to theselected spectral regions and being characteristic for the properties ofthe probe gas at operating conditions; and multiplying said spectralvector {overscore (S)} with a factor vector {overscore (V)}, said factorvector {overscore (V)} determined by calibrating measurements ofspectral vectors {overscore (S)} of calibrating gases having knownfeatures and under known conditions, in which a respective factor vector{overscore (V)} is used to determine a physical quantity based on thequality of the gas, wherein a separation formulation is carried out fordetermining the physical quantity, in which one part of the physicalquantity to be determined varies with the state and composition of theprobe gas and another part is influenced only slightly by thecomposition and state of the probe gas.
 12. Procedure according to claim11, wherein the part that is influenced only slightly with the state ofthe probe gas is calculated by determined state data coming from a knownaverage gas.
 13. Procedure according to claim 11, wherein the part thatvaries with the composition of the probe gas is determined from thetransmission spectrum of the probe gas.
 14. A procedure for determiningquality of a probe gas, comprising: determining a transmission spectrumof the probe gas at operating conditions by spectroscopical methods ofmeasurement; determining pressure p and temperature T of the probe gas;determining at least one spectral vector {overscore (S)} in a number ofselected spectral regions by integrating quantities of the transmissionspectrum of the probe gas, the spectral vector having as componentsvalues of integrals with respect to the selected spectral regions andbeing characteristic for the properties of the probe gas at operatingconditions; and multiplying said spectral vector {overscore (S)} with afactor vector {overscore (V)}, said factor vector {overscore (V)}determined by calibrating measurements of spectra vectors {overscore(S)} of calibrating gases having known features and under knownconditions, in which a respective factor vector {overscore (V)} is usedto determine a physical quantity based on the quality of the gas,wherein the physical quantity comprises a compressibility coefficient Kof the probe gas.
 15. A procedure for determining quality of a probegas, comprising: determining a transmission spectrum of the probe gas atoperating conditions by spectroscopical methods of measurement;determining pressure p and temperature T of the probe gas; determiningat least one spectral vector {overscore (S)} in a number of selectedspectral regions by integrating quantities of the transmission spectrumof the probe gas, the spectral vector having as components values ofintegrals with respect to the selected spectral regions and beingcharacteristic for the properties of the probe gas at operatingconditions; and multiplying said spectral vector {overscore (S)} with afactor vector {overscore (V)}, said factor vector {overscore (V)}determined by calibrating measurements of spectral vectors {overscore(S)} of calibrating gases having known features and under knownconditions, in which a respective factor vector {overscore (V)} is usedto determine a physical quantity based on the quality of the gas,wherein the physical quantity to be determined comprises acompressibility factor Z of the probe gas.
 16. A procedure fordetermining quality of a probe gas, comprising: determining atransmission spectrum of the probe gas at operating conditions byspectroscopical methods of measurement; determining pressure p andtemperature T of the probe gas; determining at least one spectral vector{overscore (S)} in a number of selected spectral regions by integratingquantities of the transmission spectrum of the probe gas, the spectralvector having as components values of integrals with respect to theselected spectral regions and being characteristic for the properties ofthe probe gas at operating conditions; and multiplying said spectralvector {overscore (S)} with a factor vector {overscore (V)}, said factorvector {overscore (V)} determined by calibrating measurements ofspectral vectors {overscore (S)} of calibrating gases having knownfeatures and under known conditions, in which a respective factor vector{overscore (V)} is used to determine a physical quantity based on thequality of the gas, wherein the physical quantity to be determinedcomprises a density ρ of the probe gas.
 17. A procedure for determiningquality of a probe gas, comprising: determining a transmission spectrumof the probe gas at operating conditions by spectroscopical methods ofmeasurement; determining pressure p and temperature T of the probe gas;determining at least one spectral vector {overscore (S)} in a number ofselected spectral regions by integrating quantities of the transmissionspectrum of the probe gas, the spectral vector having as componentsvalues of integrals with respect to the selected spectral regions andbeing characteristic for the properties of the probe gas at operatingconditions; and multiplying said spectral vector {overscore (S)} with afactor vector {overscore (V)}, said factor vector {overscore (V)}determined by calibrating measurements of spectral vectors {overscore(S)} of calibrating gases having known features and under knownconditions, in which a respective factor vector {overscore (V)} is usedto determine a physical quantity based on the quality of the gas,wherein the physical quantity to be determined comprises a Wobbe indexof the probe gas.
 18. A procedure for determining quality of a probegas, comprising: determining a transmission spectrum of the probe gas atoperating conditions by spectroscopical methods of measurement;determining pressure p and temperature T of the probe gas; determiningat least one spectral vector {overscore (S)} in a number of selectedspectral regions by integrating quantities of the transmission spectrumof the probe gas, the spectral vector having as components values ofintegrals with respect to the selected spectral regions and beingcharacteristic for the properties of the probe gas at operatingconditions; and multiplying said spectral vector {overscore (S)} with afactor vector {overscore (V)}, said factor vector {overscore (V)}determined by calibrating measurements of spectral vectors {overscore(S)} of calibrating gases having known features and under knownconditions, in which a respective factor vector {overscore (V)} is usedto determine a physical quantity based on the quality of the gas,wherein the physical quantity to be determined is a methane factor ofthe probe gas.
 19. A procedure for determining quality of a probe gas,comprising: determining a transmission spectrum of the probe gas atoperating conditions by spectroscopical methods of measurement;determining pressure p and temperature T of the probe gas; determiningat least one spectral vector {overscore (S)} in a number of selectedspectral regions by integrating quantities of the transmission spectrumof the probe gas, the spectral vector having as components values ofintegrals with respect to the selected spectral regions and beingcharacteristic for the properties of the probe gas at operatingconditions; and multiplying said spectral vector {overscore (S)} with afactor vector {overscore (V)}, said factor vector {overscore (V)}determined by calibrating measurements of spectral vectors {overscore(S)} of calibrating gases having known features and under knownconditions, in which a respective factor vector {overscore (V)} is usedto determine a physical quantity based on the quality of the gas,wherein the physical quantity to be determined is the molar mass of theprobe gas.
 20. A procedure for determining quality of a probe gas,comprising: determining a transmission spectrum of the probe gas atoperating conditions by spectroscopical methods of measurement;determining pressure p and temperature T of the probe gas; determiningat least one spectral vector {overscore (S)} in a number of selectedspectral regions by integrating quantities of the transmission spectrumof the probe gas, the spectral vector having as components values ofintegrals with respect to the selected spectral regions and beingcharacteristic for the properties of the probe gas at operatingconditions; and multiplying said spectral vector {overscore (S)} with afactor vector {overscore (V)}, said factor vector {overscore (V)}determined by calibrating measurements of spectral vectors {overscore(S)} of calibrating gases having known features and under knownconditions, in which a respective factor vector {overscore (V)} is usedto determine a physical quantity based on the quality of the gas,wherein the physical quantity to be determined is the density of acarbon dioxide part of the probe gas.
 21. A procedure for determiningquality of a probe gas, comprising: determining a transmission spectrumof the probe gas at operating conditions by spectroscopical methods ofmeasurement; determining pressure p and temperature T of the probe gas;determining at least one spectral vector {overscore (S)} in a number ofselected spectral regions by integrating quantities of the transmissionspectrum of the probe gas, the spectral vector having as componentsvalues of integrals with respect to the selected spectral regions andbeing characteristic for the properties of the probe gas at operatingconditions; and multiplying said spectral vector {overscore (S)} with afactor vector {overscore (V)}, said factor vector {overscore (V)}determined by calibrating measurements of spectral vectors {overscore(S)} of calibrating gases having known features and under knownconditions, in which a respective factor vector {overscore (V)} is usedto determine a physical quantity based on the quality of the gas,wherein the physical quantity to be determined is the dew point of theprobe gas.
 22. A procedure for determining quality of a probe gas,comprising: determining a transmission spectrum of the probe gas atoperating conditions by spectroscopical methods of measurement;determining pressure p and temperature T of the probe gas; determiningat least one spectral vector {overscore (S)} in a number of selectedspectral regions by integrating quantities of the transmission spectrumof the probe gas, the spectral vector having as components values ofintegrals with respect to the selected spectral regions and beingcharacteristic for the properties of the probe gas at operatingconditions; and multiplying said spectral vector {overscore (S)} with afactor vector {overscore (V)}, said factor vector {overscore (V)}determined by calibrating measurements of spectral vectors {overscore(S)} of calibrating gases having known features and under knownconditions, in which a respective factor vector {overscore (V)} is usedto determine a physical quantity based on the quality of the gas,wherein during said step of multiplying, a correcting function isincluded, said correcting function taking into account equipmentdifferences between a measurement arrangement during determination ofthe factor vectors {overscore (V)} with the calibrating gases and ameasurement arrangement during determination of the spectral vector{overscore (S)} of the probe gas.
 23. Procedure according to claim 18,wherein the measurement arrangement of the spectral vector {overscore(S)} of the probe gas is gauged for one time and results are set inaccordance with respective results of the measuring arrangement duringrecording of the factor factors {overscore (V)} with the calibratinggases.
 24. A procedure for determining quality of a probe gas,comprising: determining a transmission spectrum of the probe gas atoperating conditions by spectroscopical methods of measurement;determining pressure p and temperature T of the probe gas; determiningat least one spectral vector {overscore (S)} in a number of selectedspectral regions by integrating quantities of the transmission spectrumof the probe gas, the spectral vector having as components values ofintegrals with respect to the selected spectral regions and beingcharacteristic for the properties of the probe gas at operatingconditions; and multiplying said spectral vector {overscore (S)} with afactor vector {overscore (V)}, said factor vector {overscore (V)}determined by calibrating measurements of spectral vectors {overscore(S)} of calibrating gases having known features and under knownconditions, in which a respective factor vector {overscore (V)} is usedto determine a physical quantity based on the quality of the gas,wherein a boundary wavelength of chosen spectral regions duringrecording of the transmission spectrum is determined by appointing theboundary wavelength relative to a reference signal.
 25. Procedureaccording to claim 24, wherein a characteristic signature of thetransmission spectrum to be recorded is used as the reference signal.26. Procedure according to claim 24, wherein typical gradients ofspectrums of mediums are used as the reference signal, said gradientsbeing placed additionally in a beam path of an arrangement for measuringthe transmission spectrum.
 27. A procedure for determining quality of aprobe gas, comprising: determining a transmission spectrum of the probegas at operating conditions by spectroscopical methods of measurement;determining pressure p and temperature T of the probe gas; determiningat least one spectral vector {overscore (S)} in a number of selectedspectral regions by integrating quantities of the transmission spectrumof the probe gas, the spectral vector having as components values ofintegrals with respect to the selected spectral regions and beingcharacteristic for the properties of the probe gas at operatingconditions; and multiplying said spectral vector {overscore (S)} with afactor vector {overscore (V)}, said factor vector {overscore (V)}determined by calibrating measurements of spectral vectors {overscore(S)} of calibrating gases having known features and under knownconditions, in which a respective factor vector {overscore (V)} is usedto determine a physical quantity based on the quality of the gas,wherein among spectral regions in which the transmission spectrum of theprobe gas contains information about the composition of the probe gas,other spectral regions are surveyed in which very little or noabsorption by the gas probe occurs.
 28. Procedure according to claim 27,wherein the spectral regions in which very little or no absorptionoccurs are used for self-control of the measurement of the probe gas inthe form of a reference.
 29. Procedure according to claim 27, whereinthe spectral regions in which very little or no absorption occurs arepositioned in an area of about 1500 to 1600 nm.